Some professionals can see more than one client at a time but need a few minutes between appointments to greet their clients and begin the treatment.
Here’s a scenario in acupuncture
You offer an acupuncture treatment that lasts one hour and you can treat 4 clients at the same time. But you need 15 minutes between the beginning of each appointment.
Simply modify the options of your service to set the max clients that can be served at the same time to 4 and the delay between each appointment start to 15 minutes.